It exist systems for preparing beverages such as coffee by forcing a liquid through ingredients contained in the capsule using centrifugal forces.
WO 2008/148604 for example relates to a capsule for preparing a beverage or liquid food from a substance, in a centrifugal brewing unit, by passing water through the substance contained in the capsule by using brewing centrifugal forces comprising: an enclosure containing a predetermined dose of substance; opening means which opens under the centrifugal effect to allow the brewed liquid to leave the capsule. The capsule may also comprise means for engaging the capsule to external rotational driving means of a centrifugal brewing device wherein the engaging means are configured to offer a resistance to torque during rotation of the capsule for maintaining the capsule in a referencial rotational position.
Thereby, the effect of centrifugal forces to brew coffee or prepare other food substances presents many advantages compared to the normal brewing methods using pressure pumps. For example, in traditional espresso or lungo coffee type brewing methods using a pressure pump, it is very difficult to master all the parameters which influence the quality of extraction of delivered coffee extract. These parameters are typically the pressure, the flow rate which decreases with the pressure, the compaction of the coffee powder which also influences the flow characteristics and which depends on the coffee ground particle size, the temperature, the water flow distribution and so on. In particular, it is not easy to vary the extraction pressure and flow rates because there are essentially determined by the static pressure deliverable by the pump, the resistance of the bed of coffee and the downstream filtering system.
For a centrifugal extraction, the rotating capsule is used as a centrifugal pump. The rotational speed thus determines the flow rate of the centrifuged liquid coming out of the capsule. The quality of the beverage to be prepared depends on the control, in particular, of the flow rate. In particular, the flow rate is influenced by two parameters: the rotational speed of the capsule in the device and the back-pressure exerted on the centrifuged liquid before it is projected out of the capsule. For a given back-pressure, the higher the rotational speed, the larger the flow rate. Conversely, for a given rotational speed, the larger the back-pressure, the smaller the flow.
Whereas the rotational speed of the capsule is usually controlled by control means selectively activating a rotational motor of a centrifugal beverage production device, a predefined back-pressure is preferably obtained by a flow restriction of the centrifuged liquid at the outlet of the capsule or at the outside of a centrifugal cell carrying the capsule.
For example EP 0651 963 teaches that a pressure gradient is obtained by a rubber-elastic element interposed at the interface between the lid and the cup of the centrifugal cell. Such an element deforms elastically to leave a filtering passage for the liquid when a certain pressure is attained at the interface. The coffee grains are retained in the cell while centrifuged liquid is allowed to pass the filtering passage. Furthermore, document FR 2 487 661 and WO 2006/112691 relate to centrifugal systems wherein a fixed restriction is placed downstream of the filter to create a pressure gradient.
Moreover, WO 2008/148646 proposes a solution in which a flow restriction is placed in or outside the centrifugal cell. The flow restriction can comprise a regulating spring biased valve offering an effective back-pressure. The spring biased valve opens under the effect of a sufficient pressure of liquid exerting on the valve. The higher the speed, the larger the passage through the valve, and the higher the flow rate. The valve can be preloaded by a resilient element such as rubber or spring elements.
Therefore is a need for being able to provide beverages, (e.g. coffee) having different characteristics of intensity, taste, aroma, foam/crema in a system that is simple and versatile.
For prior art systems without back-pressure regulation, the problem is that the flow can be increased only by increasing the centrifugation speed. Therefore, this creates limits to vary the flow rate of the beverage, thereby also limiting the possibility to deliver beverages of different characteristics. Furthermore, too high rotational speeds may create problems such as noise, instability of the process, vibration and premature wearing of the mechanical pieces of the device.
The prior art beverage production systems however suffer the drawback that an adaptation of the back-pressure at the restriction valve to predefined values either requires an adjustment mechanism of the spring preconstraint in the device that makes it complex to adjust to a large variety of different predefined values of the back-pressure.
In particular, the user must adjust the spring preconstraint determining the back-pressure values before extraction, which is inconvenient in terms of usability of the device and increases the necessary preparation time.
Thereby, it is to be understood that in particular with respect to coffee beverages, the back-pressure applied on the centrifuged liquid, at a given rotational speed, determines the residence time of hot liquid (water) in contact with the coffee powder in the capsule and thereby influences directly the coffee taste and aroma. Furthermore, the organoleptic texture such as the foam/crema formed on top of the prepared beverage also depends on the applied back-pressure. Thus, with respect to the flow rate, as well as to the foam/crema, of a coffee beverage to be prepared, it is desired to adjust the values of the back-pressure imposed by the restriction valve, for instance, as a function of the type of the beverage ingredient provided in the capsule.
For example, a higher flow rate may be desired for long-volume coffee (e.g., lungo, filter coffee such as Americano) in order to avoid extraction of certain compounds that could cause bitterness to the coffee, and increase the preparation time. Vice versa, a lower flow rate may be desired for shorter coffee (e.g., ristretto or espresso).
Therefore, there is a need for a new and simpler capsule system providing the opportunity to dispense a wider choice of beverages providing different quality attributes, e.g., intensity, aroma level and/or crema, in particular, by more easily and accurately controlling the back-pressure exerted onto the centrifuged liquid.
The present invention provides a solution to the before-mentioned problems as well as offers additional benefits to the existing art.